1. Field of the Invention
This invention relates to dielectric waveguide transmission line components for millimeter wave applications and more particularly to a switchable dielectric waveguide circulator for such applications.
2. Description of the Prior Art
A problem frequently encountered in millimeter wave frequency applications which utilize dielectric waveguide transmission line components is the switching of the millimeter wave frequency signals involved. Because of the extremely small physical size of the dielectric waveguide components used in this region of the frequency spectrum, the switching function should be accomplished by a device of small physical size and which preferably consumes very little energy to accomplish the switching function. Furthermore, the design of the switching device should be as simple as possible to facilitate manufacturing of the device and to keep the manufacturing costs as low as possible. Since switches are often called upon to perform modulation functions, a suitable switching device for applications of this type should also be capable of functioning as a modulator.
Although circulators have been developed for dielectric waveguide components used in millimeter wave frequency applications, they are not usable as switching devices because the circulators themselves are not switchable. For a circulator to be switchable, the rotational direction of circulator coupling action must be easily reversed so that a signal applied to one port of the circulator may be switched to either of the adjacent circulator ports. U.S. Pat. No. 4,415,871, which was issued Nov. 15, 1983 to the applicants of the present application and which was assigned to the same assignee as the present application, shows a dielectric waveguide circulator comprising a right prism-shaped ferrite element which is magnetically biased to provide the circulator action. The magnetic biasing field which must be a unidirectional or "dc" magnetic field is applied to the bases of the prism by permanent magnets. For this circulator to be made switchable, the direction of the applied dc magnetic field must be easily reversed which, of course, is not feasible with the permanent magnet arrangement shown. Although a helically-wound coil, for example, could be utilized to produce the required unidirectional magnetic field, such a coil would require a yoke or other pole structure which would increase the size and weight of the circulator to the point where its use would no longer be desirable in millimeter wave applications where the aforementioned size and weight limitations become of critical importance. Similarly, the conventional dielectric waveguide modulators in use at the present time require wire coil arrangements which again limit their usefulness for applications in the millimeter wave frequency area of the frequency spectrum.